Published: April 2015

The following case was referred to
me by one of our former residents because of the complexity of the problem and
the combination of unfavorable factors that needed to be evaluated in regard to
diagnosis and for the formulation of a treatment plan. Several treatment
options were considered appropriate for this case and this month’s bulletin
will discuss these, together with the relative merits of each option. These
were evaluated in terms of the biomechanical level of difficulty in resolving the
impactions, the estimated prognosis of the individual teeth at the completion
of treatment and the anticipated appearance of the outcome – the patient’s
smile.

The patient was a normal, healthy
11.4 year old girl with no relevant, contributory medical history. She was
first seen in my office 2 months ago, in January 2015, when the initial
clinical examination was carried out. She arrived already equipped with
extra-oral and intra-oral clinical photographs, a panoramic film, a lateral
cephalometric film, a digitized cephalometric analysis and a CBCT series.

Fig. 1. Initial intra-oral photographs of the patient’s
dentition.

Clinical examination:

The patient had an orthognathic
profile with normal antero-posterior and vertical relations, with lip
competency and good lip cover.The
clinical intra-oral photographs showed a class 1 molar relation with a slightly
increased overbite and overjet of 2.5mm and 4.6mms respectively (Fig. 1). The
most significant feature of the dentition was the large size of the teeth and the
severe degree of dental crowding, which expressed itself in only a millimeter
of space on either side for the unerupted, non-palpable canines and a distal
angulation of the maxillary first molars. The mandibular arch was also
characterized by a general crowding, although notably less than in the maxilla.
The maxillary central incisors exhibited distally flared apex-to-crown
orientation and a minor degree of proclination. The maxillary lateral incisors
were disproportionately large and their apices were estimated to be displaced
palatally, resulting in their labially flared apex-to-crown orientations.The mandibular anterior teeth were lingually retroclined.
The maxillary deciduous second molars were still present and the second
permanent molars were unerupted

.

Fig. 2. The panoramic radiograph of the case clearly
shows the impacted canines in close association with the root apices of the
four incisors in the midline area.

Fig. 3. The lateral cephalogram shows the accurate
superimposition of the maxillary canines on each other. Similarly, the long
axes of the lateral incisors and of the central incisor on one another, is
clearly seen. The colored broken lines show the canines (orange line) on the
palatal side of the central incisors (blue line) and labial to the lateral incisors
(*yellow line).

Radiographic examination:

The panoramic view (Fig. 2), taken 2
month earlier, confirmed the large size of the erupted and unerupted teeth, all
of which were discernible, including third molars. Using root development as a
guide, the patient’s dental age was determined as being in agreement with her
chronologic age. The maxillary canines were impacted with their crown tips in
close relation to the root apices of the central and lateral incisors and close
to the midline. The film showed the presence of the two deciduous second
molars, which appeared about to shed in favor of their premolars successors. The
mandibular second molars were unerupted and their locations were considered to
be a cause for concern regarding their ability to erupt normally. This was
because of the proximity and horizontal angulation of the third molars on each
side and the mesial inclination of the right second molar. The lateral
cephalogram showed the two maxillary canines superimposed in identical
positions (Fig. 3). This film was particularly valuable, when combined with
information obtained from the panoramic view, insofar as it showed their crown
tips to be palatal to the roots of the central incisors and labial to the roots
of the lateral incisors.

Fig. 4a-c. Three different occlusally oriented views of
the maxillary arch. The axial CBCT cuts (a) depict the canine interposed
between the labially located root apices of the central incisors and the
palatally located apices of the lateral incisors. Root resorption cane clearly
be seen on the lateral incisors (arrows). The 3D screen shot (b) highlights the
entanglement of the canine crowns with the incisor roots. The clinical occlusal
photographic view of the maxilla (c) shows a degree of lingual tipping of the
central incisors, which must be interpreted as labial tipping of their
roots.In contrast, the crowns of the
lateral incisor are labially tipped and their roots therefore palpable immediately
under the palatal mucosa. Cause or result of the interposing unerupted canines?

Cone beam computerized tomography
(CBCT) examination:

Axial cuts (parallel to the
occlusal plane) of the maxillary anterior teeth at level 20 show the two
canines interposed palatal to the roots of the central incisors and labial to the
roots of the lateral incisors on each side. At this level, marked resorption of
the labial half of the root of the lateral incisors can be clearly seen (Fig.
4a). The cone beam 3D view (Fig. 4b) shows the entanglement between the incisor
apices and canines with great clarity, while the clinical occlusal view of the
upper jaw shows the contrasting orientation of the incisor crowns (Fig. 4c).

Fig. 5a-d. Cross-sectional cuts from the CBCT images show
the contrasting labio-lingual relationships between impacted canines and
incisor roots.

Cross-sectional cuts (Fig. 5a-d) confirm
the canines as being located labial to the lateral incisor roots - which are
extensively resorbed in an oblique manner (Fig. 6) - and palatal to the central incisor
roots.

Overall treatment
considerations:

As a case of class 1 skeletal and
dental relationships with large teeth and marked crowding in the
canine/premolars areas and in the retromolar areas, extraction was considered
to be mandatory in both jaws. In the mandibular dentition, a premolar on each
side would appear to be a reasonable choice to align the teeth mesial to the
first molars. In regard to the retromolar area, it is considered unlikely that
growth will provide enough additional arch length to permit a significant
improvement in the chances for the third molars being incorporated in the
erupted dentition and the need for their later extraction seems inevitable.

The complex inter-relations of the
maxillary anterior teeth seen here provide us with food for thought regarding the
influence of the choice of teeth for extraction on treatment and on quality of
outcome. These aspects are

1.difficulty of mechanotherapy,

2.Incisor root resorption

3.individual prognosis of
remaining teeth,

4.appearance.

Problem list

Aside from the fact of tooth size
and crowding, the special problems that are faced in the present case are:-

1.the complicated nature of
the relationship between the maxillary canines and the incisor roots

2.the distance of the canines
from their normal location

3.the very large lateral
incisors

4.the resorption of the roots
of the lateral incisors

Extraction options

In the mandibular dentition, extraction
of a premolar on each side is the logical way and this has to be coupled two
teeth in the maxilla. Under the present circumstances, the options are as
follows:-

a.maxillary first premolars:

Extracting the maxillary first
premolars is the treatment of choice in most orthodontic extraction cases, but
to promote this line of treatment in the present case would be a mistake, even
though this proposal is possible to complete successfully. Since the maxillary
canines and incisors are in virtually identical positions on either side in
their 3D locations in space and in relation to each other, we shall consider
them as one.

The canines are located palatal to
the roots of the central incisors and this would encourage most of us to
surgically expose them and subsequently apply traction to them on the palatal
side. However, this is to ignore the fact that the roots of the canines are
situated labial to the roots of the lateral incisors. Drawing the canines
palatally would bring their roots into contact with the labial side of the
roots of the lateral incisors and, the more the canines progressed on the
palatal side, the greater would be the displacement of the (already palatally
displaced) roots of the incisors against the palatal periosteum. The result
would be a dehiscence of the palatal aspect of the roots of the lateral
incisors and a transposed relationship between them and the canines – a
situation which will usually spell the demise of all four teeth1 ……..
and an expensive and unwinnable legal action.

The only way that these canines can
be successfully treated is to approach them from the labial side and to draw
them both labially and distally. The crowns of the central and lateral incisors
on each side are in interproximal contact. The orientation of the long axes of
the central incisors, in the crown-to-apex direction is mesial (towards the
midline suture) and slightly labial (towards the labial periosteum). The same
long axes of the lateral incisors is mesial (towards the midline suture)and strongly palatal (towards the palatal
periosteum). This means that high up in the premaxilla there is a wide bucco-lingual
space discrepancy between the apices of the central vis-à-vis the lateral
incisors, which is where the canine is located. Provided the incisors are not
uprighted or torqued in the early stages of orthodontic alignment and leveling,
this wide bucco-lingual space, or “window of opportunity”, is the key to
freeing the canine crown and, with biomechanical assistance, to permit it to
escape from its confined location, in a disto-labial direction. 2, 3

When faced with cases of this type,
it is strongly recommended that the initial leveling and alignment stage of
treatment not include distal uprighting of the central incisor nor labial root
torque of the lateral incisor. Therefore, it is recommended that the lateral
incisors remain without brackets until the canine impaction has been resolved.
For the central incisors, a straight-wire or any other form of horizontal
channel bracket should be placed at an angle that will temporarily maintain or
increase a mesial uprighting movement of the root apices. A superior
alternative is the use of a Tip Edge bracket (TP Orthodontics), which will
allow leveling, alignment and rotational movements to be performed without distal
uprighting, because of its unique slot configuration. Moreover, only round
archwires should be used. Rectangular wires of any form or variety, whether
stainless steel or nickel-titanium, are strongly contraindicated until
resolution of the impaction has been achieved, since these will “correctively”
torque the incisor roots, close off the ”window of opportunity” and thereby
further entrap the canine into an intractable position.

The risk attached to this case, in
terms of damage to the roots of the two adjacent incisors during the surgical
exposure of the canines, is very high. Obviously an open surgical exposure is
out of the question, since this would leave the roots bare and open to the oral
environment. 4 But even with a closed procedure, the proximity of
the canine crown to the incisor roots will not permit sufficient surgical
accuracy to avoid damaging the incisor root surfaces. Furthermore, attachment
bonding will be essential and the danger of etchant damage to the root surfaces,
with the likelihood of the initiation of invasive cervical root resorption, is not
to be ignored.

In addition to having to deal with
these very difficult conditions, the present case shows 2 other features which
are problematic. In the first place, the lateral incisor roots have been
markedly resorbed by their close association with the advancing canines. It has
been shown that distancing the canines from the resorption area will arrest the
resorption process. 5 However, in the present situation, the
mechanotherapy addressing the difficult location of the canines may aggravate
the resorptive process because of the initial topographical difficulty in
moving the canines away from the incisor roots. It would be imprudent to build
the future on an uncertain prognosis of the lateral incisor.

The second problematic feature is
the size of the crowns of the lateral incisors. The presence of such a broad
lateral incisor, adjacent to a similarly-sized central incisor, will present an
easily recognized flaw in the attractiveness of the patient’s eventual incisor
display and “smile esthetics”. Moreover, the presence of such a large tooth
will create a serious Bolton discrepancy although extensive interproximal
enamel reduction will largely address both these problems.

In summary, therefore, extraction
of first premolars in this case may offer a more classic dental order and a
superior appearance. However, it presents a challenging surgical exposure task
as well as giving the orthodontist an immensely demanding biomechanical problem
regarding the canines. The already resorbed lateral incisors will then need to
undergo labial root torque followed by considerable crown reduction reshaping.
In the long term analysis, approaching this case in the above manner is fraught
with technical difficulty and generates an outcome with an uncertain prognosis.

b. maxillary impacted canines:

If the decision is to extract the
permanent canines, then it is essential that this be done as soon as possible.
Their continued existence adjacent to the roots of the lateral incisor will
certainly cause further resorption and may affect the central incisors in
similar fashion. Even a skilled surgeon will not find the task easy, because of
the possibility of damage to the adjacent incisors in the cramped conditions of
their inter-relations. Given the detailed portrayal presented by the 3D images
of the CBCT, the OMFS will need to decide whether to approach the extraction
from the labial or the palatal side and whether the teeth will need to be
sectioned in order to best be eliminated.

In this way converting the
appearance of the first premolar into a more canine-like shape and reshaping
the lateral incisor, as already described above, will not present
difficulty.However, this would leave
the very young patient with two lateral incisors and their markedly shortened
roots and their re-shaped crowns with which to face the future.

By exercising this option, the
orthodontics is very much simplified, in favor of minor prosthodontic reshaping
but, here too, the patient is left with lateral incisors whose prognosis might
be fairly good in the short-to-medium term, but is uncertain long term.

Extraction of maxillary lateral
incisors is an unusual choice for extraction in orthodontics and the shock that
is likely to be registered by the patient at the loss of two of the front teeth
is not something easily understood, accepted and assuaged by any patient.
However, this bold decision has several significant advantages, the most
obvious of which is that it eliminates a priori the teeth which will end
up being the most damaged (Fig. 6) or prosthodontically altered and with the most
uncertain future. At the same time, the palatal aspect of the impacted canines
becomes freed and the teeth are no longer impacted. Although the canines are
located palatal to the central incisors, the chances of their spontaneous
eruption are almost certainly favorable …. always provided that the
orthodontist, the parents and the patient are prepared to wait! The question
here is just how long will the patient be without the teeth. It should not be
forgotten that the spaces that needs to be filled are not the canine locations,
but the lateral incisor locations and missing front teeth adjacent to the
central incisors inject a degree of urgency in resolving the impaction.

Canine teeth generally take a very
long time to erupt under normal circumstances, when their eruption path is in a
direct line to the space in the dental arch and there is space for them. It is
sometimes more than a year between the tooth first breaking through the mucosa
until it reaches its fully erupted length. One can therefore expect eruption in
this case to take considerably longer.Thus, both for the small chance that spontaneous eruption will not occur
and for the expected time lag if it does, biomechanically encouraged eruption
of the tooth should be undertaken (Fig. 7a-d).

Fig. 7a. Following extraction of the lateral incisors,
the canines were exposed on each side, immediately palatal to the central
incisors. Note the minimal degree of crown exposure and the eyelet attachment
place on the disto-labial aspect of the crown of the left canine. No attempt
was made to remove more of the follicle nor to remove bone on the labial or
mesial sides, to avoid exposing and damaging the incisor root. Surgery by Dr.
Eran Regev.

Fig. 7b. Full closure of the surgical flap in this closed
exposure procedure was performed, leaving only the twisted stainless steel
(0.014”) ligature visible.

Fig. 7c, d. The maxillary orthodontic appliance was
placed 3 weeks after the surgery. Note the use of TipEdge brackets on the
central incisors which, because of the special features of their horizontal
channel, have no uprighting effect on these teeth, as seen in these anterior
and left side views on the day the appliance was placed. Distal re-orientation
of the incisor roots would place them in the direct path of the erupting
canines. Ligation of the twisted steel connector from the unerupted canine was
made immediately to this 0.014” stainless steel archwire.

One further point that is pertinent
in any impaction case where there is concurrent crowding. This fear is always in
the back of the orthodontist’s mind when extracting erupted teeth in the
attempt to resolve the impaction of other teeth. What are the chances of
ankylosis of the canines presented in this case? Ankylosis in unerupted teeth
is uncommon, but it occurs much less frequently in the young patient. This
patient presented here is only 11.4 years of age, which is approximately when
the canines were expected to have erupted naturally. These canines have taken
an abnormal and futile “eruption” path and, as such, have travelled further
than for a normal eruption. They have also caused the resorption of the roots
of the lateral incisors to a considerable extent. Both these factors take time.
It must therefore be safely assumed that these teeth are “on the move” and that,
by mechanically redirecting their eruptive movements, the prognosis for
successful eruption would appear to be very good.

The active orthodontic treatment of
this case has only just begun and the maxillary orthodontic appliance was
placed just 2 weeks ago, which was when Fig. 7c&d were photographed. The
reason for its presentation here has been to discuss different treatment
options in cases where there are multiple adverse factors involved.I plan to update the reader with a progress
report in due course.